Field of the Invention
The present invention relates to a turbine engine with propeller(s) for an aircraft with a system for changing the pitch of the propeller.
More specifically, but not exclusively, the turbine engine is a turboshaft engine provided with contra-rotating propellers, and referred to as “open rotor” or “unducted fan”, but can also be, without departing from the scope of the invention, a turboprop engine with one propeller or a plurality of pusher propellers, with the system for changing the pitch of the vanes equally adapting to the one propeller or to each propeller of the turbine engine.
Description of the Related Art
A turbine engine of the open rotor type mainly comprises, inside a fixed cylindrical nacelle supported by the structure of the aircraft (such as the rear part of the fuselage of an aeroplane), a “gas generator” part and, aligned behind or in front of said part, a “propulsion” part. This propulsion part comprises two coaxial and contra-rotating propellers, upstream (front) and downstream (rear), respectively, that are driven, into reverse rotation relative to one another, by an epicycloidal reducer driven by a low-pressure turbine of the gas generator part, and for which the vanes of the propellers extend in a substantially radial manner outside of the nacelle.
Each propeller conventionally comprises a hub with an outer polygonal ring, rotationally received in the fixed nacelle and having radial cylindrical compartments distributed on its periphery about the longitudinal axis of the turboshaft engine. The roots of the vanes are received in the compartments of each ring.
In order to allow the optimal operation of the turboshaft engine in the various flight phases that are encountered, the vanes of the contra-rotating propellers can turn in the radial compartments of the rings. To this end, they are driven in rotation about their respective pivot axes by a suitable system allowing the setting angle of the vanes to be varied in flight, i.e. the pitch of the propellers.
This system for changing the pitch of the vanes of the propellers covers an angular range of rotation between two end positions, namely an end position referred to as a “reverse” position, in which the vanes exceed, for example, the plane transverse to the axis of the turbine engine (the direction of forward movement of the aeroplane) by 30° so as to assist with the braking of the aircraft, in the same way as conventional thrust reversers, and an end position referred to as “feathering”, in which the vanes are then feathered as much as possible relative to the direction of forward movement of the aeroplane, for example, in the event of engine failure, and thus provide the least possible resistance (drag). The angular stroke of the vanes between the feather and reverse positions is, for example, approximately 120°.
Different solutions have been proposed for changing the pitch of the vanes of propellers on “open rotor” or other types of turboshaft engines.
For example, a turboshaft engine is known from the document FR 2 908 451 in which the system for changing the orientation of the vanes of each propeller advantageously comprises a single annular actuator mounted by its cylinder on the ring hub of the propeller, whereas its piston is linked, via a linking mechanism of the system associated with the actuator, to the roots of the various vanes. The displacement of the piston following the fluidic control of the annular actuator provides the required angular pivoting of the vanes by the linking mechanism by varying their pitch.
Even though this provides satisfactory results, such a solution involves an annular actuator and thus a cylinder, which is a fixed part, and a piston rod, which is a movable part, with a large diameter since it is assembled on the same hub as the propeller, as well as a mass that is necessarily high due to its large diameter, especially since it then has to be reinforced in order to withstand the centrifugal forces and to avoid the risks of ovalisation caused by the rotation of the associated propeller.
Furthermore, deformations and sealing problems tend to appear due to the rotating mounting of the annular actuator on the hub of the propeller and the fluidic elements used (rotating seals, etc.) in this extreme environment (significant mechanical and thermal stresses, high rotation speed, etc.). Finally, the linking mechanism of the system, which is composed of ball joints on the roots of the vanes and receptacles sliding in an annular groove of the piston, leads to wear phenomena that must be monitored during use in order to prevent the risk of jamming.
A mechanism for changing the pitch of an aeroplane propeller assembly is also known from the document FR2551023.